This invention relates to apparatus for reducing the noise made by the circulation of an endless drive chain about a drive sprocket and idler and more particularly to apparatus for reducing track noise in a track-type vehicle.
A major source of noise in the operation of a track-type vehicle is the tracks as they pass over the drive sprockets, front idlers and carrier rollers. Most of such track noise is generated by the impacting of the links and pintles of the drive chain incorporated in the track against the drive sprockets, idlers and rollers as the track is circulated during movement of the vehicle. Since the drive chain of the track is made of links which have a finite length, a true rolling motion is not achieved as the track passes around the drive sprockets and idlers and over the rollers. Instead, each link defines a chord in the circular motion of the track about the drive sprockets and idlers and the links pivot with respect to each other causing the pintles thereof to tend to impact against the drive sprockets and idlers as they enter into engagement therewith and the ends and pintles of the links to impact against the rollers as they pass thereover.
Where it is possible to tension the drive chain as by mounting the drive sprockets and idlers with their axes resiliently positioned with respect to each other in order to hold the drive chain taut, the above described source of noise may be avoided. However, in those applications requiring that the axes of the drive sprockets and idlers be rigidly mounted with respect to each other, a catenary will be present in the drive chain and the above described impacting action of the links and pintles against the drive sprockets and idlers will occur, resulting in the generation of noise.
It is common practice to use carrier rollers to support or reverse the catenary present in the chain. However, even where the carrier rollers are spring loaded in an attempt to tension the drive chain, the mass of the individual links is sufficient to produce impacts against the carrier rollers in addition to the drive sprocket and idler tending to add sources of noise generation.
Various attempts have been made in the prior art to reduce such noise by damping either the impact or the noise resulting from such impact. For example, drive sprockets and idlers filled with sand to damp the noise made by the impact of the links of the drive chain thereon have been proposed. However, it is not desirable to add to the size and weight of the sprockets and idlers or to reduce their structural strength by making them hollow to accommodate a noise damping material.
It is an object of this invention to reduce the noise made by circulation of an endless drive chain about a drive sprocket and idler without requiring structural modification of the drive sprocket and idler.
It has also been proposed to place energy absorbing material such as rubber between the drive chain and the drive sprockets and idlers associated therewith in order to damp the impact therebetween. For example, rings of rubber have been bonded to the peripheries of the sprockets, idlers and rollers for engagement by the drive chain. Although this method is effective in reducing the noise, it has been found that the wear of the rubber in operation is excessive, resulting in an impractically short life.
Similarly, it has been proposed that alternate teeth of the drive sprocket be dummy teeth made of rubber in order to absorb the impact energy of the links of the drive chain as they engage the sprocket. This approach is also effective in reducing noise but again, excessive wear results in an operating life too short to be practical.
It is another object of this invention to provide apparatus for reducing the noise made by circulation of an endless drive chain about a drive sprocket and idler which will have an operating life approaching that of the drive chain itself.
It is a further object of this invention to provide a apparatus for reducing the noise made by circulation of an endless drive chain about a drive sprocket and idler which will tend to recover the energy ordinarily lost in the impact of the drive chain on the sprocket and idler.
It is yet another object of this invention to provide a simple, inexpensive and easy to maintain apparatus for reducing the noise made by the circulation of an endless drive chain about a drive sprocket and idler which apparatus will have long life in operation and will exhibit a reduced tendency to be inactivated or become clogged during operation in mud, sand or under other severe environmental conditions.